PREDICTORS OF DIFFICULT INTUBATION: STUDY IN KASHMIRI POPULATION

Transcription

1 Original article Pravara Med Rev 2009; 1(4) PREDICTORS OF DIFFICULT INTUBATION: STUDY IN KASHMIRI POPULATION Gupta A K, Ommid Mohamad, Nengroo Showkat, Naqash Imtiyaz, Mehta Anjali ABSTRACT Airway assessment is the most important aspect of Anaesthesia practice as a difficult intubation may be unanticipated. A prospective study was done to compare the efficacy of airway parameters to predict difficult intubation viz; degree of head extension, thyromental, inter incisor gap, grading of prognathism, obesity and modified mallampati test. Six hundred patients with ASA I& ASA II grade were enrolled in study. All patients were preoperatively assessed for airway parameters. Intra-operatively all patients were classified according to Cormack and Lehane laryngoscopic view. Clinical data of each test was collected, tabulated and analyzed to obtain the sensitivity, specificity, positive predictive value & negative predictive value. Results obtained showed incidence of difficult intubation in 3.3%. Head& neck movements had the highest sensitivity (86.36%); high arched palate had highest specificity (99.38%). Head & neck movements had highest sensitivity; high arched palate had highest specificity, however, head & neck movements strongly correlated for patients with difficult intubation. Keywords: Intubation, Anaesthesia, Laryngoscopy INTRODUCTION The fundamental responsibility of an anesthesiologist is to maintain adequate gas exchange. In order to do this, the airway must be managed in such a way that it is almost continuously patent. Failure to maintain a patent airway for more than a few minutes results in brain damage or death [1]. Anaesthesia in a patient with a difficult airway can lead to both direct airway trauma and morbidity from hypoxia and hypercarbia. Direct airway trauma occurs because the management of the difficult airway often involves the application of more physical force to the patient s airway than is normally used. Much of the morbidity specifically attributable to managing a difficult airway comes from an interruption Address for correspondence: Dr.Arun Kumar Gupta, Astt.Prof., Dept. of Anaesthesiology & Critical Care, Rural Medical College, Loni Maharashtra, India, guptaarun71@yahoo.com of gas exchange (hypoxia and hypercapnia), which may then cause brain damage and cardiovascular activation or depression [2]. Though anesthesiologist is a final authority in the technique of Endotracheal Intubation, there will be hardly any such specialist who might not be experiencing occasional difficulties in this life saving technique. As difficult Intubation occurs infrequently and is not easy to define, research has been directed at predicting difficult laryngoscopy, this is graded as the portion of larynx seen when a Macintosh laryngoscope is used in a patient. It is argued that, if difficult laryngoscopy has been predicted and intubation is essential, skilled assistance and special equipment should be provided. Although the incidence of difficult or failed tracheal intubation is comparatively low, unexpected difficulties and poorly managed situation may produce a life threatening condition or even death [3]. 12

2 Difficulty in intubation is usually associated with difficulty in exposing the glottis by direct laryngoscopy. This involves a series of maneuvers like extending the head, opening the mouth, displacing and compressing the tongue into the submandibular space and lifting the mandible forward. The ease or difficulty in performing each of these maneuvers can be assessed by one or more parameters [4]. Extension of head at the atlanto-occipital joint can be assessed by simply looking at the movements of the head, measurement of sternomental or by using devices to measure the angle [5]. Mouth opening can be assessed by measuring the between upper and lower incisors with the mouth fully open. The ease of lifting the mandible can be assessed by comparing the relative position of the lower incisors in comparison with the upper incisors after forward protrusion of the mandible [6]. The measurement of mento-hyoid and thyromental provide a rough estimate of the submandibular space [7]. The ability of the patient to move the lower incisor in front of the upper incisor tells us about jaw movement. The classification provided by et al [8] and later modified by Samsoon and Young [9] help to assess the size of tongue relative to oropharynx. Abnormalities in one or more of these parameters may help predict difficulty in direct laryngoscopy [1]. Initial studies tried to compare individual parameters to predict difficult intubation with mixed results [8,9]. Later studies have attempted to create a scoring system [3,10] or a complex mathematical model [11,12]. This study is an attempt to verify which of these factors are significantly associated with difficult exposure of glottis and to rank them according to the strength of association. MATERIALS & METHODS The study was conducted after obtaining institutional review board approval. Six hundred ASA I & II adult patients, scheduled for various elective procedures under general anesthesia, were included in the study after obtaining informed consent. Patients with gross abnormalities of the airway were excluded from the study. All patients were assessed the evening before surgery by a single observer. The details of airway assessment are given in Table I. Airway Parameter Modified Method of assessment Class I: Faucial pillars, soft palate and uvula visible. Class II: Soft palate and base of uvula seen Class III: Only soft palate visible. Class IV: Soft palate not seen Class I & II : Easy Intubation Class III & IV: Difficult Intubation Obesity Obese BMI (= 25) Non Obese BMI (< 25) Inter Incisor Gap Degree of Head Extension Grading of Prognathism Distance between the incisors with mouth fully open(cms) Distance between the tip of thyroid cartilage and tip of chin, with fully extended(cms) Grade I = 90 0 Grade II = Grade III < 80 0 Class A: - Lower incisor protruded anterior to the upper incisor. Class B: - Lower incisor brought edge to edge with upper incisor but not anterior to them. Class C: - Lower incisors could be brought edge to edge. Table I: Method of assessment of various airway parameters (predictors) 13

3 In addition the patients were also examined for the following and if present were recorded accordingly. High arched palate. Protruding maximally incisor (Buck teeth) Wide & short Neck Direct laryngoscopy with Macintosh blade was done by an anesthetist who was blinded to preoperative assessment. Glottic exposure was graded as per Cormack- Lehane classification 13 (Fig 1): Figure 1: Cormack-Lehane grading of glottic exposure on direct laryngoscopy GRADE 1: Most of the glottis visible GRADE 2: Only the posterior extremity of the glottis and the epiglottis visible GRADE 3: No part of the glottis visible, only the epiglottis seen GRADE 4: Not even the epiglottis seen Grades 1 and 2 were considered as easy and grades 3 and 4 as difficult. RESULTS Glottic exposure on direct laryngoscopy was difficult in 20 (3.3%) patients. The frequency of patients in various categories of predictor variables is given in Table-II The association between different variables and difficulty in intubation was evaluated using the chi-square test for qualitative data and the student s test for quantitative data, p<0.05 was regarded as significant. Airway Parameter Modified Group Class 1&2 Class 3&4 Obesity Obese BMI (> 25) Non Obese BMI (< 25) Inter Incisor Gap Head & Neck Movements Grading of Prognathism Wide and Short neck Class I : >4cm Class II: <4cm Class I: > 6cm. Class II: < 6cm. Difficult {class II & III (90 0 )} Easy {class I(>90 0 )} Difficult (class III) Easy (class I + II) Normal neck body ratio 1:13 Difficult (Ratio>1:13) Freque ncy (%) 96% 4% 28.7% 71.3% 93.5% 6.5% 94.6% 5.4% 16% 84% 96.1% 3.9% 86.9% 13.1% High arched Yes 1.9% Palate No 98.1% Protruding Yes 4.2% Incisors No 95.8% Table II: The frequency analysis of predictor parameters Clinical data of each test was collected, tabulated and analyzed to obtain the sensitivity, specificity, positive predictive value & negative predictive value. Comparative analysis of sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of various physical factors and scoring systems are given in Table III. 14

4 Physical factors and various Systems Sensitivity Specificity PPV NPV Obesity Inter incisor gap Head and Neck movement Prognathism Wide and Short neck High arched palate Protruding incisor scoring system Cormack and Lehane s scoring system Table III: Comparative analysis of various physical factors and scoring systems DISCUSSION Difficulty in endotracheal intubation constitutes an essential predisposing factor of morbidity and mortality, especially when it is not anticipated preoperatively. This unexpected difficulty in intubation is probably the result of a lack of accurate predictive tests and inadequate preoperative assessment of the airway. Risk factors if identified at the preoperative visit help to alert the anesthesiologist so that alternative methods of securing the airway can be used or additional expertise sort before hand. Direct laryngoscopy is the gold standard for tracheal intubation. There is no single definition of difficult intubation. Difficult glottic view on direct laryngoscopy is the most common cause of difficult intubation. The incidence of difficult intubation in this study is similar to that of others. As for as the predictors are concerned there are wide variations. Restriction of head and neck movement and decreased mandibular space has been identified as important predictors in other studies as well. classification has been reported to be a good predictor by many but found to be of limited value by others [14]. Interincisor gap, forward movement of jaw and thyromental produce variable results in previous studies [7,15]. Even though thyromental is a measure of mandibular space, it is influenced by degree of head extension. There have been attempts to create various scores in the past. Many of them could not be reproduced by others or of limited practical value. Complicated mathematical models based on clinical and/or radiological parameters have been proposed by few in the past [16], but these are difficult to understand and tough to follow in clinical setting. Many of these studies consider all the parameters of equal importance. Instead of trying to find ideal predictor(s), score or model, we simply arrange them in an order based on the strength of association with difficult intubation. Restricted extension of head, decreased thyromental and poor class are significantly associated with difficult intubation. In other words patients with decreased head extension have much higher probability of having a difficult intubation compared to those with abnormality in other parameters. The type of equipments needed to manage can be chosen according to the parameter which is abnormal. For example in a patient with decreased mandibular space, it may be prudent to choose devices which do not involve displacement of the tongue like Bullard laryngoscope or Fiber-optic laryngoscope. Similarly in patients with decreased head extension devices like McCoy Larngoscope are likely to be more successful. CONCLUSION This prospective study tests the efficacy of various parameters of airway assessment as predictors of difficult intubation. We have find out that head & neck 15

5 movements, high arched palate, thyromental & Modified Malampatti test are the best predictors of difficult intubation. REFERENCES 1. Rose DK, Cohen MM. The airway: problems and predictions in 18,500 patients. Can J Anaesth 1994; 41: Benumof JL: Management of the difficult airway: With special emphasis on awake tracheal intubation. Anesthesiology 1991; 75: Wilson ME, Spiegelhalter D, Robertson JA, Lesser P. Predicting difficult intubation. Br J Anaesth 1988; 61(2): A.Vasudevan, A.S.Badhe. Predictors of difficult intubation a simple approach. The Internet Journal of Anesthesiology 2009; 20(2) 5. Tse JC, Rimm EB, Hussain A. Predicting difficult endotracheal intubation in surgical patients scheduled for general anesthesia: a prospective blind study. Anesth Analg 1995; 81(2): Savva D. Prediction of difficult tracheal intubation. Br J Anaesth 1994; 73(2): Butler PJ, Dhara SS. Prediction of difficult laryngoscopy: an assessment of the thyromental and predictive tests. Anaesth Intensive Care 1992; 20(2): SR, Gatt SP, Gugino LD, Desai SP, Waraksa B, Freiberger D, et al. A clinical sign to predict difficult tracheal intubation: a prospective study. Can Anaesth Soc J 1985; 32(4): Samsoon GL, Young JR. Difficult tracheal intubation: a retrospective study. Anaesthesia 1987; 42(5): Nath G, Sekar M. Predicting difficult intubation a comprehensive scoring system. Anaesth Intensive Care 1997; 25(5): Charters P. Analysis of mathematical model for osseous factors in difficult intubation. Can J Anaesth 1994; 41(7): Arne J, Descoins P, Fusciardi J, Ingrand P, Ferrier B, Boudigues D, et al. Preoperative assessment for difficult intubation in general and ENT surgery: predictive value of a clinical multivariate risk index. Br J Anaesth 1998; 80(2): Cormack RS, Lehane J. Difficult tracheal intubation in obstetrics. Anaesthesia 1984; 39(11): Lee A, Fan LT, Gin T, Karmakar MK, Ngan Kee WD. A systematic review (meta-analysis) of the accuracy of the tests to predict the difficult airway. Anesth Analg 2006; 102(6): Bilgin H, Ozyurt G. Screening tests for predicting difficult intubation. A clinical assessment in Turkish pat ients. Anaesth Intensive Care 1998; 26(4): Naguib M, Malabarey T, AlSatli RA, Al Damegh S, Samarkandi AH. Predictive models for difficult laryngoscopy and intubation. A clinical, radiologic and three-dimensional computer imaging study. Can J Anaesth 1999; 46(8):